1. Field of invention
The present invention relates to a device for measuring a light absorption material in blood which serves to emit a light onto a living tissue, to process a signal based on an intensity of a transmitted light or a reflected light, thereby detecting information about the light absorption material in blood such as an oxygen saturation.
2. Related art
In the device of this kind, in the case in which a noise made by a body movement or a probe slip-off is mixed into a signal based on the intensity of the transmitted light or the reflected light, a signal measured previously is subjected to an averaging process. Based thereon, for example, an oxygen saturation or a pulse rate is calculated.
Furthermore, in the case in which a large noise is made or a noise is mixed for a long period of time, an oxygen saturation and a pulse rate which are obtained before the mixture of the noise are retained and displayed.
However, if a measured value obtained before the mixture of the noise is used, a change in the oxygen saturation or the pulse rate cannot be known at the present time. Consequently, there is a possibility that a critical condition might be missed.
The present invention has been made to avoid such a situation and has an object to remove a noise in a signal processing based on an intensity of a transmitted light or a reflected light for a living tissue, thereby accurately obtaining information about a light absorption material in blood.
A first aspect of the invention is directed to a device for measuring a light absorption material in blood comprising light emitting means for emitting lights having a plurality of different wavelengths onto a living tissue, light receiving means for receiving a transmitted light or a reflected light for the living tissue from the light emitting means and for outputting a signal corresponding to an intensity thereof, D.C./A.C. detecting means for obtaining a D.C. component and an A.C. component for a signal corresponding to each wavelength which is the output signal of the light receiving means, respectively, A.C. to D.C. ratio detecting means for obtaining an A.C. to D.C. ratio signal which is a ratio of the A.C. component to the D.C. component for each wavelength calculated by the D.C./A.C. detecting means, component extracting means for extracting a component having a predetermined frequency or more for the A.C. to D.C. ratio signal having each wavelength which is obtained by the A.C. to D.C. ratio detecting means, extracted component ratio detecting means for obtaining a mutual ratio of an extracted component signal having each wavelength which is extracted by the component extracting means, and means for detecting information about a light absorption material in blood based on the ratio detected by the extracted component ratio detecting means.
Consequently, the ratio detected by the extracted component ratio detecting means can be set to a ratio of wavelengths of only a noise signal. Furthermore, the ratio can be regarded as equal over the whole frequency range of the A.C. to D.C. ratio signal obtained by a measurement. Therefore, if the A.C. to D.C. ratio signal is processed by using the ratio in place of the noise signal, the processing can be simplified.
A second aspect of the invention is directed to the device for measuring a light absorption material in blood according to the first aspect of the invention, wherein the information detecting means serves to detect an ideal signal assumed when the A.C. to D.C. ratio signal has no noise based on a predetermined relationship among the ratio detected by the extracted component ratio detecting means, the A.C. to D.C. ratio signal detected by the A.C. to D.C. ratio detecting means and the ideal signal, and to detect the information about the light absorption material in blood.
Consequently, the ideal signal is obtained without a noise signal. Therefore, information about a desirable light absorption material in blood can be obtained with high precision.
A third aspect of the invention is directed to a device for measuring a light absorption material in blood, comprising light emitting means for emitting lights having a plurality of different wavelengths onto a living tissue, light receiving means for receiving a transmitted light or a reflected light for the living tissue from the light emitting means and for outputting a signal corresponding to an intensity thereof, D.C./A.C. detecting means for obtaining a D.C. component and an A.C. component for a signal corresponding to each wavelength which is the output signal of the light receiving means, A.C. to D.C. ratio detecting means for obtaining an A.C. to D.C. ratio signal which is a ratio of the A.C. component to the D.C. component for each wavelength calculated by the D.C./A.C. detecting means, noise condition deciding means for deciding at least whether a high frequency component of a noise included in the A.C. to D.C. ratio signal is large, and a plurality of signal processing means provided corresponding to a result of the decision of the noise condition deciding means respectively for processing the A.C. to D.C. ratio signal having each wavelength which is obtained by the A.C. to D.C. ratio detecting means, thereby detecting information about a light absorption material in blood, the signal processing means provided corresponding to a case in which the noise condition deciding means decides that the high frequency component of the noise is large, including component extracting means for extracting a component having a predetermined frequency or more for the A.C. to D.C. ratio signal having each wavelength which is obtained by the A.C. to D.C. ratio detecting means, extracted component ratio detecting means for obtaining a mutual ratio of an extracted component signal having each wavelength which is extracted by the component extracting means, and means for detecting information about a light absorption material in blood based on the ratio detected by the extracted component ratio detecting means.
Consequently, different processings are carried out depending on the noise condition. Therefore, a result of a measurement can be obtained with higher precision. In particular, in the case in which. the high frequency component of the noise is large, the same function can be obtained because of the same structure according to the first aspect of the invention.
A fourth aspect of the invention is directed to the device for measuring a light absorption material in blood according to the third aspect of the invention, wherein the information detecting means serves to detect an ideal signal assumed when the A.C. to D.C. ratio signal has no noise based on a predetermined relationship among the ratio detected by the extracted component ratio detecting means, the A.C. to D.C. ratio signal detected by the A.C. to D.C. ratio detecting means and the ideal signal, and to detect the information about the light absorption material in blood.
Since the structure is the same as that in the second aspect of the invention, the same function can be obtained.
A fifth aspect of the invention is directed to the device for measuring a light absorption material in blood according to the second or fourth aspect of the invention, further comprising pulse rate detecting means for detecting a pulse rate based on the ideal signal. Consequently, the pulse rate can also be detected in addition to the information about the light absorption material in blood.
A sixth aspect of the invention is directed to the device for measuring a light absorption material in blood according to the second or fourth aspect of the invention, further comprising display means for displaying a waveform of the ideal signal. Consequently, a pulse signal having no noise is displayed.
A seventh aspect of the invention is directed to the device for measuring a light absorption material in blood according to the first or third aspect of the invention, the predetermined frequency is a substantially pulsation frequency of living tissue.
An eighth aspect of the invention is directed to the structure in which the information about the light absorption material in blood is an oxygen saturation. Consequently, the oxygen saturation can be measured with high precision.
A ninth aspect of the invention is directed to the structure in which two wavelengths are used as the different wavelengths.